The invention relates to inks for ink jet printing.
Ink jet printing, for example, drop-on-demand ink jet printing, involves forming characters on a substrate by ejecting ink droplets from a printhead having one or more nozzles.
The inks may be hot melt inks that are solids at room temperature but liquids at jetting temperatures. Hot melt inks are in widespread use in ink jet printers.
Hot melt inks can have some potential drawbacks. Hot melt inks are solid at room temperature, and it is necessary to heat the inks in order to apply them to the substrates. Heating may cause the components of the ink to degrade, which may cause the ink jets to clog.
In addition, hot melt inks may be partially or fully worn off the surface of a substrate after they solidify in response to, for example, rubbing, scratching, or flexing. Hot melt inks may also cause offsetting; offsetting occurs when ink is applied to one surface, that surface contacts another surface, and an unwanted image is formed on the second surface.
Wax has often been used in hot melt inks. Wax provides the ink with the property of being solid at room temperature, but liquid at elevated temperatures. Wax can be brittle at room temperature, however, which may lead to poor adhesion of the ink to the substrate. The problem of poor adhesion may be compounded when the wax shrinks upon cooling to room temperature, disturbing the mechanical bonds between the substrate and the ink.